Waste chemicals generated by, for example, industrial plants, are often disposed of by injecting the chemicals into disposal wells that penetrate subterranean zones (also called formations). Suitable subterranean zones for receiving such waste chemicals are separated by natural barriers from other subterranean zones containing useful resources such as oil, gas, and water. Wells that penetrate subterranean zones have traditionally been formed by drilling a well bore down to the subterranean zone, followed by placing a string of metal pipe, e.g., casing, in the well bore. A hydraulic cement slurry is pumped downwardly through the interior of the pipe and upwardly through the annulus, which is located between the exterior of the pipe and the walls of the well bore. The cement slurry in the annulus is permitted to set, i.e., harden into a solid mass, thereby attaching the string of pipe to the walls of the well bore and sealing the annulus.
Unfortunately, many waste chemicals injected into disposal wells, such as organic materials, acidic materials, caustic materials, and salt water, are corrosive to the hydraulic cement in the well bore. Moreover, hydrogen sulfide and carbon dioxide gases generated by the subterranean zone or injected into the disposal well can lead to degradation of the hydraulic cement. In particular, hydrogen sulfide corrodes the cement, and carbon dioxide reacts with calcium in the cement when exposed to temperatures exceeding 200° F., which are often encountered in the well bore, thus forming calcium carbonate. The high downhole temperatures in the well bore can accelerate this degradation of the hydraulic cement. As a result of the degradation of the hydraulic cement in the annulus, the waste chemicals injected into the disposal well can undesirably leak into subterranean zones containing useful fluids such as water that could otherwise be used as drinking water.
In order to overcome the foregoing problem, epoxy-based compositions having the ability to resist degradation by chemicals have been developed to replace hydraulic cements used in disposal wells. While the epoxy-based compositions are highly resistant to degradation, they suffer from the limitation that their curing times are relatively short at temperatures of 300° F. or higher. Such temperatures are commonly encountered down in the disposal well. The curing times of the epoxy-based compositions are therefore too short for the compositions to be properly placed in the annulus such that they can isolate laterally adjacent subterranean zones from waste chemicals injected into the disposal well. In particular, as an epoxy-based composition is being pumped down the pipe in the disposal well, at least a portion of it hardens, never reaching the annulus. In addition, any epoxy-based composition that becomes cured in the annulus, such that it attaches the string of pipe to the walls of the well bore, can soften again under the relatively high downhole temperatures. As a result, the epoxy-based composition may fail to hold the string of pipe in place.
A need therefore exists for a chemically resistant sealant composition having a curing time long enough to allow it to be properly placed in the annulus. Further, it would be desirable if the sealant composition would remain in the hardened state despite being exposed to relatively high temperatures.